This invention relates to devices for use in the practice of dentistry and more particularly to dental x-ray film holding devices. The primary function of such devices is to hold x-ray film securely and in proper alignment with the teeth, and in some cases in proper alignment with both the teeth and the x-ray apparatus during x-ray procedures. While in the past, some devices have employed dental impression type materials to maintain the alignment of the x-ray film (as in U.S. Pat. No. 1,899,877) or to help secure the x-ray holder in the mouth (as in U.S. Pat. No. 1,585,264); contemporary, x-ray film holding devices generally rely on the patient's ability to maintain a steady bite on the x-ray film holder to achieve these objectives. The present invention relates to holders of this latter type.
X-ray holders which are presently available possess a number of shortcomings. Most are uncomfortable and none adequately account for the effect of patient comfort and bite pressure on the quality of the x-ray negatives produced.
In order to explain the deficiencies in the present art, it is first necessary to define terms of compressibility. For purposes of this specification and claims, a material will be said to be compressible if, in the range of compressive pressures typical of a dental patient's bite, a material will be substantially compressed in its linear dimension, as measured along a line perpendicular to the pressure imparting surfaces. A material will be said to be incompressible if, in the range of compressive pressures typical of a patient's bite, the material will not be substantially compressed in its linear dimension, as measured along a line perpendicular to the pressure imparting surfaces. A material will be said to be elastically compressible if, upon a relaxation of compressive pressure, the compressed material will recover its original linear dimension with little or no hysteresis. Finally, a material will be said to be deformably compressible if, upon a relaxation of compressive pressure, the compressed material will experience significant hysteresis.
The one-piece x-ray holders such as those described in U.S. Pat. Nos. 3,444,371 and 3,936,643 are deficient in that their structure is, for all practical purposes, completely defined by a single elastically compressible material. Because these holders must function both as film holder and bite plate, the material of construction must be sufficiently rigid to maintain a predetermined alignment of x-ray film and holder, while at the same time be sufficiently elastically compressible to allow the device to be gripped securely by the teeth. The compromise necessary to serve these two desired ends with but a single structural component, results in an x-ray holder which serves neither desired end well. A further shortcoming of these one-piece holders is that none are designed to function cooperatively with the latest generation of x-ray equipment which utilizes x-ray cone positioning devices. A further shortcoming of the one-piece holder is that either the whole unit must be disposable, which can be costly; or the whole unit must be designed to maintain its structural integrity and compressibility in the face of repeated sterilization. Both of these limitations are costly, and the latter places a severe constraint on the scope of possible materials of construction.